Dawn Redwood, approximately 10 years old, 30 ft tall, I have two of these in...
Dawn Redwood, approximately 10 years old, 30 ft tall, I have two of these in my back yard and they are both affected. It was first noticed about a month ago. They both live in full sun on a slight embankment. My lawn was sprayed once earlier this year for weeds but the trees have never had any fertilizer or pesticide.
The picture is helpful but not enough to provide a definitive diagnosis. Dawn redwoods are typically disease free but it’s possible that it is suffering from needle cast. The link below will provide some additional information on this disease. The pictures on the fact page resemble the diseased needles on the picture you submitted. .
Dawn redwoods drop their needles in the fall but I believe it is to early for that to begin. You might be interested in this link about dawn redwoods:
The only pest typically associated with dawn redwoods are Japanese beetles. Have you noticed a heavy infestation of beetles around the trees?
My recommendation would be to take a sample of the diseased branch and a healthy branch nearby to your local extension office for closer examination to see if they can determine if there are any identifiable fungi on the undersides of the needles that provide a clue.
York County Extension office
112 Pleasant Acres Road
York, PA 17402-9041